The "Hit the Lights" singer, who looked radiant in a Dsquared2 dress and Herve Leger heels, was serenaded by dozens of celebrities -- including Taylor Swift, 22, Josh Hutcherson, 19, Ellen DeGeneres, 54, Zooey Deschanel, 32, and Jonah Hill, 28 -- after collecting a surfboard for Choice Music Group at the Teen Choice Awards in Universal City, Calif., on July 22.

As the star-studded crowd sang "Happy Birthday," Gomez blew out sparkler-topped cupcakes, which she later shared with audience members. "This is the best birthday present ever," Gomez told those gathered at the Gibson Amphitheater in Los Angeles.

Later in the show, an eyewitness spotted Gomez and Swift "bobbing their heads" as the "Wizards of Waverly Place" star's boyfriend, Justin Bieber, 18, performed a medley of "Boyfriend" and "As Long as You Love Me."

Post-show, Gomez and Bieber had a romantic dinner at Il Cielo in Beverly Hills, Calif. "Selena walked out the front holding hands with Justin and she was holding a bouquet of flowers," a source tells Us Weekly.

On July 23, Gomez raved about her unforgettable day via Facebook. "Beyond blessed. So much love," she wrote. "Thank you for the most incredible birthday yet! I'm truly, truly grateful. I love my family, friends and all of you."